Add zpop example.

redis/conn_test.go

@@ -402,5 +402,4 @@ func ExampleDial(x int) {
 		// handle error
 	}
 	defer c.Close()
-
 }

redis/zpop_example_test.go

@@ -0,0 +1,113 @@
+// Copyright 2013 Gary Burd
+//
+// Licensed under the Apache License, Version 2.0 (the "License"): you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations
+// under the License.
+
+package redis_test
+
+import (
+	"fmt"
+
+	"github.com/garyburd/redigo/redis"
+)
+
+// zpop pops a value from the ZSET key using WATCH/MULTI/EXEC commands.
+func zpop(c redis.Conn, key string) (result string, err error) {
+
+	defer func() {
+		// Return connection to normal state on error.
+		if err != nil {
+			c.Do("DISCARD")
+		}
+	}()
+
+	// Loop until transaction is successful.
+	for {
+		if _, err := c.Do("WATCH", key); err != nil {
+			return "", err
+		}
+
+		members, err := redis.Strings(c.Do("ZRANGE", key, 0, 0))
+		if err != nil {
+			return "", err
+		}
+		if len(members) != 1 {
+			return "", redis.ErrNil
+		}
+
+		c.Send("MULTI")
+		c.Send("ZREM", key, members[0])
+		queued, err := c.Do("EXEC")
+		if err != nil {
+			return "", err
+		}
+
+		if queued != nil {
+			result = members[0]
+			break
+		}
+	}
+
+	return result, nil
+}
+
+// zpopScript pops a value from a ZSET.
+var zpopScript = redis.NewScript(1, `
+    redis.log(redis.LOG_WARNING, KEYS[1])
+    local r = redis.call('ZRANGE', KEYS[1], 0, 0)
+    redis.log(redis.LOG_WARNING, #r)
+    if r ~= nil then
+        r = r[1]
+        redis.call('ZREM', KEYS[1], r)
+    end
+    return r
+`)
+
+// This example implements ZPOP as described at http://redis.io/topics/transactions.
+func Example_zpop() {
+	c, err := dial()
+	if err != nil {
+		panic(err)
+	}
+	defer c.Close()
+
+	// Add test data using a pipeline.
+
+	for i, member := range []string{"red", "blue", "green"} {
+		c.Send("ZADD", "zset", i, member)
+	}
+	if _, err := c.Do(""); err != nil {
+		panic(err)
+	}
+
+	// Pop using WATCH/MULTI/EXEC
+
+	v, err := zpop(c, "zset")
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println(v)
+
+	// Pop using a script. The script is simpler and faster.
+
+	v, err = redis.String(zpopScript.Do(c, "zset"))
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println(v)
+
+	// Output:
+	// red
+	// blue
+}